The field of the disclosure relates generally to multiphase electrical machines and, more particularly, to an electrical machine operable as a multiphase motor and a multiphase generator and a method of use thereof.
Many known electrical systems perform both electrical motoring and generation during the course of normal operation. For example, and without limitation, certain vehicle power systems, such as aircraft power systems, include electrical machines that are utilized as a motor for propulsion and may also be utilized as electrical generators. While motoring, electrical power from an auxiliary source is applied to the electrical machine to turn a rotor attached to a mechanical load. Mechanical loads include, for example, and without limitation, turning a drive shaft to start an engine or to accelerate a vehicle. Auxiliary power sources include, for example, and without limitation, various alternating current (AC) and direct current (DC) power sources, such as AC grid power, a battery, a photovoltaic array, or any other suitable power source for the mechanical load. While generating, a prime mover turns the rotor to generate AC power. The generated AC power is then distributed to one or more AC or DC loads.
AC power generated by a particular known electrical machine is typically produced at a particular voltage and with one or more phases. Such AC power is then converted by a transformer to an appropriate voltage level to power a given AC load, and further converted by a rectifier to DC to power a given DC load. Rectifying AC power to DC power generally yields higher quality DC power when the AC power is multiphase, e.g., 3-phase, 6-phase, and 12-phase. For example, phase-shifted outputs of the rectifier combine to produce low-ripple voltages and currents due to cancellation of phase-shifted harmonics. Likewise, motoring under auxiliary power typically utilizes single- or 3-phase power. Consequently, an electrical machine that both motors and generates typically does so with 3-phase power.
Many known electrical systems that utilize the known motor-generator electrical machines described above generally include additional power electronics to perform the necessary motoring and generating functions. For example, and without limitation, a known aircraft power system may include an auto-transformer rectifier unit (ATRU) including an auto-transformer unit (ATU) and a rectifier. When generating, the ATU converts generated 3-phase power to a higher-order multiphase power, i.e., 6-phase or more. The multiphase power is then rectified to DC and distributed to the AC or DC electrical loads. The additional power electronics used for converting to multiphase power and then to DC power are often nearly as heavy as the electrical machine itself. The additional weight in the electrical system reduces efficiency. Further, the necessary transformers and rectifiers typically introduce losses themselves, including, for example, and without limitation, commutation losses and parasitic losses.